There are various uses for heat exchangers known in the art. For instance, heat exchangers, referred to as charge air coolers, use a coolant, such as water, to cool compressed air exiting a turbocharger before the air is moved into an engine cylinder. The compressed air flowing from the turbocharger can reach high temperatures. For example, it is not uncommon for the compressed air exiting the turbocharger to reach 240° C. Due to the high temperature, the compressed air has a lower density, and thus, less oxygen than an identical volume of colder compressed air. In order to increase the air density, and thus the amount of oxygen that can be burned within the engine, the hot compressed air will flow through air passages within the charge air cooler. The heat within the air can be exchanged with coolant flowing through coolant passages adjacent, and often perpendicular, to the air passages within the charge air cooler. Therefore, the coolant will increase in temperature and the air will decrease in temperature as the coolant and air simultaneously pass through the charge air cooler.
Although the charge air coolers used in conjunction with turbochargers do cool the compressed air prior to entering the engine, the heat exchange between the air and the coolant can sometimes result in corrosion within the coolant passages of the charge air cooler. Often, the corrosion occurs in the coolant passages nearest the hot air inlet because the air within the charge air cooler is at its highest temperature when entering the charge air cooler. The hot compressed air can boil the coolant, and the boiling coolant can erode the metal around the coolant passages. Eventually, the boiling coolant can create a hole between the coolant and air passages, allowing leakage between the two. This leakage can undesirably cause coolant to enter an engine cylinder.
It is foreseeable that the risk of corrosion within the liquid passages will increase as the capabilities of turbochargers improve. Engineers are continually attempting to increase engine power by improving the air compression capability of turbochargers. However, increased compression results in increased temperature of the exiting compressed air. For instance, it is foreseeable that turbochargers will soon be producing compressed air at 300° C. The increased temperature of the compressed air may not only cause coolant to boil within the coolant passage adjacent to the hot air inlet, but may be sufficient to cause the coolant within the coolant passages farther away from the hot air inlet to also boil.
Engineers have attempted to reduce corrosion within heat exchangers by various methods. For instance, a charge air cooler described in published U.S. Patent Application No. 2002/0011242 A1, includes multiple heat exchanger blocks. A first heat exchanger block is included within a different coolant circuit than a second heat exchanger block. The first heat exchanger block uses a higher temperature coolant and a more erosive resistant and temperature stable material than the second heat exchanger block. Thus, the first heat exchanger block acts as a pre-cooler of the compressed hot air prior to its entry into the second heat exchanger block. Although the described charge air cooler may reduce the amount of corrosion caused by boiling coolant, manufacturing the charge air cooler may be expensive and burdensome. For instance, the higher temperature coolant and the corrosion resistant material may increase the costs of manufacturing and operating the charge air cooler, and may require two separate coolant systems. In addition, using two heat exchanger blocks may increase the size of the charge air cooler such that it consumes valuable space in a chassis.
The present invention is directed at overcoming one or more of the problems set forth above.